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Full text of "Handbook Of Chemical Engineering - I"

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184
CHEMICAL ENGINEERING
air compressed per minute, pi the initial pressure and pz the final pressure, pounds per square foot. To get the actual horsepower at the shaft, the horsepower should be divided by the efficiency, which will vary from 0.60 to 0.80. If the speed remains unchanged, owing to the small clearances, the horsepower tends to increase tremendously with decrease in orifice.
The so called Hytor compressor (or exhaust) Fig. 38, works on the principle of a number of columns of liquid acting acting as pistons between the rotor teeth. The casing is ovoid and as the moving liquid swings away from the rotor shaft the gas is
FIG. 38.  Hytor compressor.
drawn into the space vacated.   As the liquid swings back further in the revolution the gas is compressed and tends to escape through the outlets.
The efficiency is high but the effluent gas will always be saturated with the vapor of the liquid used as the circulating medium.
CHIMNEYS
Chimney draft is based upon the difference of specific gravity of cold air and heated air. The column of warm air in the chimney exerts a pressure per square foot at the base of hdij where h is the height in feet and d\ is the density of hot gases in pounds per cubic foot. The pressure of the outside air for the same height is hdz, where d% is the density of cold air in pounds per cubic foot. The motive force is therefore the difference of these two, or h(dz  <#i), in pounds per square foot.
For ordinary calculations,
77.84     7.95\
Where H = height of chimney in feet, Di = intensity of draft, inches of water, TI  absolute Fahrenheit temperature of chimney gases, T* = absolute Fahrenheit temperature of outside air, and PI = observed atmospheric pressure, pounds per square inch. For high altitudes above sea level: